1. Field of Invention
The invention relates to a hybrid type vehicle driving controller, a hybrid type vehicle driving control method and its program.
2. Description of Related Art
In a hybrid type vehicle having a planetary gear unit in which, e.g., a sun gear, a ring gear and a carrier are arranged, the carrier and an engine are connected, the ring gear and a drive wheel are connected, and the sun gear and an electric generator are connected, the torque of the engine, i.e., one portion of the engine torque TE is transmitted to the electric generator, and the remaining torque is transmitted to the drive wheel together with the torque of a drive motor, i.e., drive motor torque TM.
In the hybrid type vehicle of this type, the electric generator is connected to the engine through the planetary gear unit. When an operating point of the engine, as an engine target operating state, is determined, the engine torque TE at the operating point is determined as engine target torque TE* showing a target value of the engine torque TE. The rotating speed of the engine at the operating point, i.e., an engine rotating speed NE is determined as an engine target rotating speed NE* showing a target value of the engine rotating speed NE.
The rotating speed of the electric generator, i.e., an electric generator target rotating speed NG* showing a target value of an electric generator rotating speed NG is calculated on the basis of the engine target rotating speed NE*. The torque of the electric generator, i.e., electric generator torque TG, is controlled such that the electric generator rotating speed NG becomes the electric generator target rotating speed NG*.
When the electric generator rotating speed NG is suddenly raised and the voltage of a battery, i.e., a battery voltage VB is reduced, the engine races and an excessive rotating state is caused.
FIG. 2 is a view showing the relationship of the electric generator rotating speed and the electric generator torque in the conventional hybrid type vehicle. In this figure, the electric generator rotating speed NG is set on the axis of the abscissa, and the electric generator torque TG is set on the axis of the ordinate.
Reference numerals L1 to L3 designate lines showing the relationship of the electric generator rotating speed NG, the electric generator torque TG and the battery voltage VB. As the battery voltage VB is reduced, characteristics are changed in the direction of an arrow B. As the battery voltage VB is raised, the characteristics are changed in the direction of an arrow A.
When the electric generator is operated at a driving point p1 on the line L2 in FIG. 2 and, for example, a driver suddenly applies brakes, the rotating speed of the ring gear connected to the drive wheel is suddenly reduced. Thus, the electric generator rotating speed NG is suddenly raised and the electric generator is operated at a driving point p2. As a result, because the electric generator torque TG is suddenly reduced, the engine rotating speed NE cannot be restrained by the electric generator torque TG. Therefore, the engine rotating speed NE is suddenly raised, the engine races and the excessive rotating state is caused.
Further, when the electric generator is operated at the driving point p1 and the battery voltage VB is reduced, the electric generator is operated at a driving point p3. Because the electric generator torque TG is also suddenly reduced in this case, the engine torque TE cannot be restrained by the electric generator torque TG. Therefore, the engine rotating speed NE is suddenly raised, the engine races and the excessive rotating state is caused.
Therefore, a hybrid type vehicle driving controller is arranged to prevent the engine from attaining the excessive rotating state, and various kinds of excessive rotation preventing controls are performed in the hybrid type vehicle driving controller.
Namely, in a first excessive rotation preventing control, an electric generator maximum rotating speed NGmax showing a maximum value of the electric generator rotating speed NG is set to correspond to the battery voltage VB. As the battery voltage VB is reduced, the electric generator maximum rotating speed NGmax is set to be reduced. As the battery voltage VB is raised, the electric generator maximum rotating speed NGmax is set to be raised. The engine is prevented from attaining the excessive rotating state by limiting the electric generator target rotating speed NG* so as not to exceed the electric generator maximum rotating speed NGmax.
There is a case in which the actual electric generator rotating speed NG becomes higher than the electric generator target rotating speed NG* when the electric generator target rotating speed NG* is limited in the first excessive rotation preventing control. Therefore, in a second excessive rotation preventing control, an electric generator maximum torque TGmax showing a maximum value of the electric generator torque TG is calculated corresponding to the battery voltage VB and the temperature of an inverter. An engine maximum torque TEmax, showing a maximum value of the engine torque TE, is set from the electric generator maximum torque TGmax and a gear ratio γGE from the electric generator to the engine. The engine is prevented from attaining the excessive rotating state by limiting a throttle aperture θ of the engine such that the engine torque TE does not exceed the engine maximum torque TEmax.
When the engine cannot be prevented from attaining the excessive rotating state by performing the first and second excessive rotation prevention controls, fail safe control is performed so as not to exceed an electric generator limit rotating speed NGlim (e.g., 6000 [rpm]) setting a mechanical limit rotating speed of the electric generator.
Namely, in the fail safe control, it is judged whether the electric generator rotating speed NG reaches the electric generator limit rotating speed NGlim. When the electric generator rotating speed NG reaches the electric generator limit rotating speed NGlim, the engine torque TE is compulsorily limited, the fuel supplied to the engine is cut by 100[%], and the electric generator is shut down. The fail safe control is performed to protect the electric generator, and behavior, vibration, operability, etc. of the hybrid type vehicle are not considered.
However, when the hybrid type vehicle runs in a cold place, the internal resistance of the battery is increased so that the change in the battery voltage VB becomes large. Therefore, there is a case in which the battery voltage VB is suddenly reduced as the hybrid type vehicle is suddenly accelerated. In this case, the electric generator torque TG is reduced even when the first and second excessive rotation preventing controls are performed. Therefore, it is difficult to restrain the engine torque TE, and it is impossible to prevent the engine from attaining the excessive rotating state.
Further, when the hybrid type vehicle runs across roads having friction coefficients different from each other, e.g., when the hybrid type vehicle is moved from a road having a small friction coefficient with ice on its surface to a road having a large friction coefficient as in asphalt, the shaft of the driven wheel is locked and the rotating speed of the ring gear connected to the drive wheel is suddenly reduced so that the electric generator rotating speed NG is suddenly raised.
Accordingly, when the battery voltage VB is suddenly reduced and the electric generator rotating speed NG is suddenly raised, the first and second excessive rotation preventing controls cannot be reliably performed. As its result, it is impossible to reliably prevent the engine from attaining the excessive rotating state.
Therefore, the engine target torque TE* is calculated on the basis of the electric generator target torque TG* showing a target value of the electric generator torque TG and the electric generator maximum torque TGmax (e.g., see JP-A-2001-304010).
However, in the above conventional hybrid type vehicle driving controller, it is impossible to reliably prevent the engine from attaining the excessive rotating state when it is difficult to restrain the engine torque TE by the electric generator torque TG due to individual differences in the engine, the electric generator, etc., and a calculating error of the electric generator target torque TG*, the electric generator maximum torque TGmax, etc.